The Dark Tower isn't SUPPOSED to be scary, silly. You just have to look at it as a totally different genre for SK. I've read the series 3, maybe 4, times and have listened to it on audio CD.
My favorite of his scarier books is The Shining. My husband is reading that one for the first time now. I also really liked Bag of Bones, which wasn't really scary - but it was a nice love story.
The Stand is strongly intertwined with the Dark Tower. So is Insomnia, which I'm rereading right now.